Field of the Invention
The present invention relates to a shielded wire and a wire harness.
Description of Related Art
Conventionally, a shield braid configured by braiding metal coated fibers in each of which a metal film is formed on the outer circumference of a refractory fiber, copper members made of copper or a copper alloy being placed between a plurality of metal coated fibers constituting the braid, at a constant thickness has been proposed (see Patent Literature 1: JP-A-2013-110053). According to the shield braid, while high bendability is realized by the metal coated fibers, the grounding process is enabled by the copper members to be easily performed, and, when the thickness of the copper members is made adequate, the bendability can be prevented from being lowered by an excessive thickness of the copper members.
[Patent Literature 1] JP-A-2013-110053
According to a related art, in a shield braid, no consideration is given to a sheath which is disposed on an outer circumference of the shield braid, and, even when the shield braid itself has a high bendability, there is a possibility that the bendability may be lowered by the influence of the sheath. In the case where the shield braid is bent, for example, the degree of freedom is lost because of the contractile force of the sheath, and therefore there is a possibility that the wires may be broken at an early stage. In such a case, the shielding performance is lowered, and the bending resistance of the whole of the shielded wire including the sheath cannot be improved.
One or more embodiments provide a shielded wire and a wire harness in which bending resistance can be improved.
In accordance with one or more embodiments, a shielded wire includes an electrical wire including a conductor portion and a covering portion, a shield braid in which electrically conductive wire members are braided, and which covers an outer circumference of the electrical wire, and a tubular sheath disposed on an outer circumference of the shield braid and made of an insulating resin,
wherein D1 is an inner diameter of the sheath in a state where the sheath is disposed on the outer circumference of the shield braid,
wherein t is a thickness of the sheath in the state where the sheath is disposed on the outer circumference of the shield braid,
wherein E is a modulus of elasticity of the sheath,
wherein μA is a coefficient of static friction between the shield braid and the electrical wire,
wherein μB is a coefficient of static friction between the shield braid and the sheath,
wherein Fmax is a value of a load which, in a fatigue test where a load is repeatedly applied to the shield braid in an axial direction of the braid, is obtained when an electrical resistance value of the shield braid is increased by 10% with respect to an initial value at a timing when the load is repeatedly applied 5 million times,
wherein D2 is an inner diameter of the sheath in a free state, and
wherein D2 satisfies following relational expression (1).
                                          D            ⁢                                                  ⁢            1                    -                                    D              ⁢                                                          ⁢                              1                2                            ⁢                                                F                  ⁢                                                                                        max                            ×                              10                4                                                    π              ⁢                                                          ⁢                              tE                ⁡                                  (                                                            μ                      A                                        +                                          μ                      B                                                        )                                                                    ≦                  D          ⁢                                          ⁢          2                <                  D          ⁢                                          ⁢          1                                    (        1        )            
According to one or more embodiments, the inner diameter D2 of the sheath in the free state satisfies the above-described relational expression, and therefore it is possible to reduce the possibility that the constriction of the shield braid is excessively enhanced by contraction of the sheath, and the electrically conductive wire member is broken before 5 million endurance cycles. Therefore, the bending resistance of the whole shielded wire can be improved.
In the wire harness of one or more embodiments, the wire harness may include the above mentioned shielded wire.
The wire harness includes the shielded wire in which the bending resistance is improved, and therefore also the bending resistance of the whole wire harness can be improved.
According to one or more embodiments, it is possible to provide a shielded wire and wire harness in which the bending resistance can be improved.